This Application is a U.S. National Phase Application of PCT International Application PCT/JP99/05530.
The present invention relates to a manufacturing method of circuit board and a porous sheet, more specifically a manufacturing method of circuit board comprising a process of filling a conductive material in pierced holes of the, plate for circuit board, a manufacturing apparatus and a porous sheet used for it.
A manufacturing method of circuit board has a process of forming pierced holes (through holes) in said plate serving as base material of circuit board and a printing process for printing conductive material on that plate. This printing process comprises a process of forming a conductive layer of prescribed pattern on the surface of said plate, and a process of filling a conductive material in said pierced holes (metallizing process) to ensure electric continuity between the both surfaces of said plate. Conventionally, for filling the conductive material sufficiently in the pierced holes in the latter metallizing process, the plate for circuit board was placed on the printing stage and, while the pierced holes in the plate were vacuum sucked, the conductive material was filled in the pierced holes. FIG. 4 indicates that conventional method. As shown in FIG. 4, air intake ports 37 are formed on a printing stage 32, and the air intake ports 37 have holes slightly larger than the pierced holes 36. At the position where the air intake ports 37 correspond to the pierced holes 36, a plate 31 for circuit board is placed on the printing stage 32. In this state, vacuum suction is performed from under the printing stage 32. With this Vacuum suction, the air in the pierced holes 36 is sucked through these air intake ports 37. In this state, the conductive material 35 put on a screen mesh 33 placed on the plate 31 for circuit board is screen printed. In the screen process printing, the conductive material 35 is printed inside the pierced holes 36 through a screen mesh 33 by means of a squeegee 34. As a result of this screen process printing, the conductive material 35 is filled in the pierced holes 36.
However, in the conventional printing process described above, each time when the position of pierced holes 36 in the plate 31 for circuit board changes, the position of the air intake ports 37 in the printing stage 32 must also be changed. For that reason, the manufacturing cost of the printing stage 32 becomes high. Moreover, in said conventional method, part of the conductive material 35 filled in the pierced holes 36 moves into the air intake ports 37. For that reason, as the number of times of printing process increases, the conductive material 35 gradually accumulates in the air intake ports 37. When the number of times of printing process further increased, the conductive material 35 also passed to the back side of the plate 31, producing a deposit of dirt there, and the conductive material 35 was transferred to the surrounding area on the bottom face side of the pierced holes 36 and, as a result, said method caused occurrence of short-circuit in the circuit board.
The present invention provides a manufacturing method of circuit board, not requiring any change of specifications of the printing stage at each change of specifications of the plate for circuit board nor producing any dirt on the back side of the plate for circuit board, and a porous sheet used it.
The manufacturing method of circuit board according to the present invention comprises:
(a) a process of feeding a printing stage having a porous member permeable in the direction of thickness,
(b) a process of placing a plate for circuit board having pierced holes above said porous member, and
(c) a process of filling a conductive material in said pierced holes from the upper side of said plate for circuit board by sucking said porous member at prescribed vacuum pressure from the back side of said porous member.
The manufacturing apparatus of circuit board according to the present invention comprises a printing stage having a porous member permeable in the direction of thickness,
a suction mechanism for sucking said porous member at prescribed vacuum pressure from the back side of said porous member, and
a coating mechanism for coating a conductive material on said plate for circuit board placed on said printing stage, from the upper side of said printing stage,
in which the plate for circuit board may be placed above said porous member, and
makes it possible for said conductive material to be coated on the surface of said plate for circuit board from the upper side of said plate while said plate is being sucked as said porous member is vacuum sucked from the back face side of said printing stage.
Particularly preferably, said porous plate plays the role of said printing stage.
Particularly preferably, said porous member has a porous plate permeable in the direction of thickness and a porous sheet permeable in the direction of thickness placed on said porous plate, and said plate is placed on the upper side of said porous sheet.
Particularly preferably, said porous sheet is replaceable and, moreover, a process of replacing said porous sheet is provided.
Particularly preferably, said porous sheet contains cellulose in the range of approximately 90 wt % to approximately 98 wt %, and said cellulose contains softwood kraft pulp in the range of approximately 20 wt % to approximately 40 wt % and hardwood kraft pulp in the range of approximately 60 wt % to approximately 80 wt %.
With the construction described above, there is no more need of changing the specifications of porous plate and porous sheet as printing stage each time when the specifications of the plate for circuit board are changed, and it becomes possible to fill a conductive material easily in pierced holes of the base material for circuit board with different specifications. Furthermore, adhesion of conductive material and dirt to the back face of the plate for circuit board is prevented.